1. Field of the Invention
The present invention relates to a variable compression ratio apparatus. More particularly, the present invention relates to a variable compression ratio apparatus that changes compression ratio of an air-fuel mixture in a combustion chamber according to a driving condition of an engine.
2. Description of Related Art
Generally, thermal efficiency of combustion engines increases as a compression ratio thereof increases, and if ignition timing is advanced to some degree, thermal efficiency of spark-ignition engines increases. However, if the ignition timing of the spark-ignition engines is advanced at a high compression ratio, abnormal combustion may occur and the engine may be damaged. Thus, the ignition timing cannot be advanced a lot and accordingly engine output may deteriorate.
A variable compression ratio (VCR) apparatus changes the compression ratio of an air-fuel mixture according to a driving state of an engine. The variable compression ratio apparatus raises the compression ratio of the air-fuel mixture at a low-load condition of the engine in order to improve fuel mileage. On the contrary, the variable compression ratio apparatus lowers the compression ratio of the air-fuel mixture at a high-load condition of the engine in order to prevent occurrence of knocking and improve engine output.
A conventional variable compression ratio apparatus includes a connecting rod connected to a piston and receiving combustion force of the air-fuel mixture, a pin link receiving the combustion force of the air-fuel mixture from the connecting rod and rotating a crankshaft, and control means changing a rotation trace of the pin link according to the driving condition of the engine. According to the conventional variable compression ratio apparatus, the compression ratio of the air-fuel mixture changes as the rotation trace of the pin link changes.
According to a conventional variable compression ratio apparatus, the control means are disposed vertically under the crankshaft or are disposed horizontally next to the crankshaft. Therefore, volume of the crank case may increase.
In addition, the compression ratio of the air-fuel mixture changes but stroke and exhaust amount does not change according to the conventional variable compression ratio apparatus.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.